The Rift Valley fever epizootic in Egypt 1977-78. 2. Ecological and entomological studies.

Epidemiological factors related to the introduction, spread and maintenance of Rift Valley fever (RVF) virus were studied during the 1977-78 epizootic in Egypt, Culex pipiens is the most ubiquitous and prevalent mosquito species in the Nile Valley and Delta. Isolation of RVF virus from unengorged C. pipiens, and demonstration of laboratory transmission of the virus by this species, strongly implicate it as the chief vector in Egypt. Virus transmission to man also occurs by contamination when handling infected meat and by inhaling natural virus aerosols. Wild rodents apparently do not serve as RVF virus reservoirs. Domestic sheep, cattle, buffaloes, camels, goats, donkeys and dogs act as amplifying hosts. Over 30% of the camels sampled at the southern border of Egypt were serologically positive for antibodies to RVF virus and it appears likely that the virus was introduced into Egypt, either by these animals or by other vehicles from the south.